Children of Poseidon
by AmaltheaLuchiaAizen
Summary: What if Percy wasn't the only Demigod child of Poseidon? what if he had a younger half sister that not even his father knew about due to a one stand drunken stand? What if she was the Girl who Lived on the run from England? how would that change The story as we know it? (Based on the movie universe!) Percy is 15 and FemHarry is 14! takes place after fourth year!
1. Chapter 1

Amalthea: *cackles evilly* Ok I finally watched the two Percy Jackson movies and read my Harry potter books right after which inspired this story! So please enjoy this Crossover! KON HIT IT!

KON: Amalthea does not own The Harry Potter series, Percy Jackson Series or any songs that appear in this fanfic. All she owns is the idea, Pairing, Family ties and her version of Fem-harry. Please vote in her poll plus Read and review her stories! Now On to SPARTA...I mean...ON TO THE STORY! Enjoy this little plot bunny!

Ch.1

14 year old Marina Potter gasped for breath as she raced to the Wizard bank with Dumbledore and they made it inside just in time, they were quickly shown to a private room with a table and few cozy chairs as the goblin in charge of her account came in and said "We do not have much time, Lady Potter... We must do the test now and get you out of the country due to Fudge's stupidity."

Marina nodded and she quickly cut her palm on the dagger that the Goblin handed her as the blood dripped onto the paper, they watched as words appeared on the paper and Marina Jawdropped as her true heritage was revealed...

_Inheritance test for Marina Potter_

_Father: Poseidon, God of the Sea_

_James potter: Blood Adopted_

_Mother: Lily Evans_

_**Inherited powers and abilities:**_

_Animagus: Horse, doe and Water phoenix_

_Water and Wind elemental_

_Able to breathe under water_

_Inhuman Reflexes_

_Siren like singing voice (when channeling magic into throat)_

_Affinity for languages_

_**Other relatives:**_

_Percy Jackson: Half brother through Poseidon_

_Petunia Dursley: Aunt_

_Dudley Dursley: Cousin_

_Hades, lord of the Underworld: Uncle_

_Zeus, ruler of Olympus: Uncle_

Marina stared at the paper in disbelief then the Goblin gulped and said "You being a half blood, my lady, seem to make a lot of sense on how you survived..."

"What do you mean Half Blood?"

Dumbledore looked at his adoptive granddaughter and said with a sad smile "it means you're a demi god...they are hard to kill through magic which explains why you've been so lucky in your adventures."

The goblin then spoke up and said "There is a camp in the states where you would be able to live without fear of the ministry finding you. I can arrange for you to be placed as close as possible to it or I can send you to your half brother in hopes no one would look there for you..."

Marina thought about it quickly then nodded as she said "I want to get to know my brother...and if he winds up going to the camp then I'll go too!"

"I understand My Lady; we must get you there soon! Have you got everything?"

Marina nodded as her owl then swooped in and landed on her arm, Hedwig hooted as Marina said good bye to Dumbledore with tears in her eyes then gently took the port key as the Account manager said the password. Marina and Hedwig then stumbled as she landed in the mouth of an alley near an apartment block, Marina looked at Hedwig and smiled as she said "Go fly, girl and be careful!"

Hedwig nuzzled her then flew into the sky as Marina looked at the paper in her hand and realized that it had the Apartment block and Apartment number on it. She sighed in relief and hurried over to the Apartment block as she headed in with her bag and came to the apartment, She took a deep breath and knocked as a pretty black haired woman answered the door and asked "May I help you?"

Sally looked at the familiar looking girl and Jawdropped as the girl said "Are...are you Sally Jackson, Percy's mom?"

"Yes but why are you...here?"

The girl seemed incredibly nervous and said "I'm Percy's half Sister by our dad..."

Sally looked shocked and said "Oh my god...please come in!"

"Thank you..."

Sally quickly got some tea ready for the both of them and sat down with Marina as she asked "How is this possible?"

Marina blushed and said "From what Sirius, my godfather said when I first found out the guy I believed to be my dad wasn't...it was a drunken one night stand after my mom had a big fight with my Step father and dad was upset about leaving his family..."

Sally had to smile as the young girl was kind and polite and she said "for now we'll pass you off as Percy's cousin from England that came to live with us."

"Thank you...Aunt Sally."

Sally smiled and said "I hope you don't mind the couch to sleep on for now...all of our rooms are filled up."

Marina smiled and told her it was fine as they heard suddenly "Mom, I'm home!"

Marina watched as a boy who looked almost exactly like her except with blue eyes and somewhat curly black hair, walked into the living room and paused in surprise. Sally quickly introduced Marina as his cousin from England and then she said "Marina...this is your Cousin, Percy."

Marina stood and said "It's a pleasure to meet you..."

Percy smiled and shook her hand as he returned the gesture; they then started talking happily about their favorite books and movies as Percy sat on the couch with her. Marina was overjoyed to find her brother liked most of the same books she liked to read and said "I'm really glad I came here, Percy..."

Percy chuckled and said "I am too. You're a lot of fun to talk with!"

Marina grinned then noticed Sally was getting prepared to cook dinner and said "Aunt Sally...I'm willing to cook if you want any help."

Sally smiled and said "I'm fine but you can help me tomorrow."

Marina smiled as her and Percy then continued talking...

Two weeks later...

Marina was in the museum with her brother when she noticed the sub that gave her a bad vibe, was taking her brother into an unfinished part of the museum. She quickly followed and slipped into the room as she drew her wand, she watched as the Sub revealed her true form then before the creature could attack Percy and harm him, Marina fired a cutting curse into the creature's side. The creature screamed in pain as Grover and Mr. Bruner came in and she made to attack Marina and Percy, Marina quickly fired off a warning shot with a stunner as she stood in front of her brother with cold eyes looking at the creature.

The two males watched in shock as the new girl easily held off the Fury with her wand, Mr. Bruner then called to the creature and told it to leave before he ripped it to pieces. Marina looked at the two and chuckled as the fury left and then helped her brother up, she watched as Percy was given a "pen" by the older male and they hurried back to the apartment with Grover in front. Marina and the two boys entered the apartment as the man Percy and Sally lived with, then pinned Percy against the wall for disrespecting him. Before Grover could do anything to help Percy, Marina had pulled the man back and broke his nose with a well aimed punch as she snarled "Touch him again and you'll regret it!"

Sally looked amused until Grover said "Sally... It's time!"

Marina, Grover, Percy and Sally were all in the car when Percy kept questioning what was going on, Marina then listened as Percy was told about his father and how he was forced to leave him and Sally. Percy then said "Ok but what about Marina? You used some kind of stick to fend off the fury creature..."

Marina sighed and said "Well I was in training as a magic user in England before the idiot in charge of my headmaster and the school I went to, decided to order me to be killed for something I didn't do..."

Percy blinked in shock then said "You mean Magic is real?"

"Yep, that creature wasn't one I've encountered before but I have faced a Cerberus and lived..."

Grover looked at her in shock as he squeaked "YOU faced a Cerberus and lived?"

Marina nodded and said "I was eleven when that happened..."

Suddenly a cow came out of nowhere and landed in front of the car as they barely missed hitting it but caused the car to flip, Marina groaned in pain as she said "Anybody catch the number of that bus?"

They then noticed something heading towards the car as Grover revealed his true form as a Satyr and kicked out the glass in the window, they quickly got out and ran for the woods with Grover urging them on. They soon saw the gate and ran through only to have Sally hit a barrier before entering, Percy tried to get her through when the creature chasing them revealed itself to be a Minotaur and Marina swore as it caught Sally then it made her disappear into thin air. Marina quickly helped Percy defeat the Minotaur before she caught him from blacking out from killing the creature; Marina helped Grover take Percy to the infirmary where they were met by Mr. Bruner who was in his real form of a centaur. He raised an eyebrow at her lack of Reaction to his form as she then yawned after making sure Percy was comfortable, Chiron then realized how much Marina looked like Percy for the first time since he met her and thought to himself "It can't be..."

Marina looked over at Chiron and smiled as she said "You have the same look my friend Hermione gets when she has a question...What is it that you want to ask me?"

"Do you know who your Godly parent was?"

"I didn't know until two weeks ago...when I took an inheritance test at Gringotts..."

Chiron looked surprised then asked "Who did it show?"

Marina smiled sadly and said "I can tell you already know do to how you look at me and Percy...but where Percy was probably planned, I wasn't...I'm the result of a one night drunken stand..."

Chiron winced and asked "Just how old are you?"

"I'm 14 but I'll be 15 on the 31st of July."

Chiron did the math and winced as he said "It must have been quite the drink to make Poseidon that damn drunk..."

Marina grinned and said "Well from what I found out...he was in a magic user bar..."

Chiron couldn't help but laugh and say "Aye, that would do it..."

Chiron then placed a hand on her shoulder and said "Does Percy know yet?"

Marina shook her head and said "We're going to tell him everything after the museum trip but you saw how that worked out..."

Chiron nodded then said "Why don't you get some sleep, Marina...something tells me you need it..."

Marina nodded as she placed her head on the bed and quickly fell into a light sleep while Chiron covered her with a soft blanket...

Three days later...

Percy groaned as he woke up and Grover asked him what he remembered, Percy told him and jumped as he realized it was no dream like he just thought it was. Just then Marina poked her head in and grinned at seeing Percy wake, She hugged him and said teasingly "Welcome back to the world of the living..."

Percy returned the Hug and Marina took a deep breath as Percy asked "So what's going on? Why were you able to go past the barrier when mom wasn't?"

Marina then sighed and said "Percy do you remember how your Mom hesitated when she said I was your cousin?"

"Yeah...what does this have to do with that barrier?"

"I'm not your cousin but I am still related to you..."

Percy looked confused as Marina then took a deep breath and said "I'm actually your half sister through our dad..."

Percy's and Grover's eyes nearly popped out of their heads at that and then Percy said "But why did you lie to me?

Marina then told him everything that had happened in her school years at Hogwarts and a bit of her upbringing at her aunt's after her mother and stepfather were killed, she then said "we were actually going to tell you after the trip to the museum but as you can see...that didn't go as planned."

Percy smiled and pulled Marina into a hug which she gladly returned then they walked out of the infirmary and they told Percy about where they were and what purpose it served, Percy looked a little overwhelmed at all the info until they went and saw Chiron...

Two hours later...

Marina and Percy were picked for the blue team by a Young man named Luke who was the son of Hermes, Marina grinned happily at hearing the game was capture the flag and was raring to go as Chiron gave the signal to start. Marina quickly followed her brother and Luke past the battle with most of the red and blue team, they were quickly engaged in a fight that Luke dominated and told them to go look for the Flag. Marina grinned evilly as her and her brother then stopped at a stream so Percy could have a drink when she and Percy spotted the Red team's flag, Percy then walked towards it while Marina made sure she wasn't seen. Percy then was attacked by Annabeth and was seemingly defeated as Marina then jumped out in an over head attack, Annabeth was taken by surprise but quickly began to fight back against Marina as Percy made his way to the water and stuck his hand in...

Later that night

Marina laughed softly as she sat in a tree overlooking the party when she noticed the central fire grow much bigger suddenly and revealed a devil like creature that was on fire. She watched as Fire balls were thrown at targets then she recognized the voice of a man who had saved her from her cousin a few times while he visited England, She jumped to the ground and ran over to the creature as she said "Uncle Hads, is that you?!"

Hades froze at that old nickname and turned to the girl who smiled happily and said "I KNEW I recognized your voice!"

"Marina? What are you doing in America?"

"Fudge is what happened; He gave the order to have me killed for something I didn't do...much like how Percy never stole the lightning bolt..."

Hades looked at the girl he had saved so long ago and asked "What were you accused of doing?"

"Murdering Cedric Diggory when it was Voldemort who did it...He somehow came back through some kind of Dark Ritual using my blood, his father's bones and the flesh of a servant doing the ritual..."

Hades and Chiron paled at those words then Hades said "That Bastard!"

Marina looked amused and said "Better not let Auntie hear you swear in front of me yet again..."

The demi-gods all started chuckling at that as Hades said "Don't remind me..."

Hades then talked to Percy quickly about his mother being alive and what he had to do to get her back, Marina and Grover then caught the look Percy sent them as Marina kept herself from grinning evilly. Marina was quick to pack her bag along with Percy and then they made to sneak out when Annabeth and Grover joined them, Marina grinned evilly when Grover asked "How are we going to get to the Underworld?"

Annabeth then led them to Luke as she asked him how his dad would get to and from the underworld...

One hour later...

Marina giggled as Percy and Grover got into a Thumb war to both girls' amusement, Marina then yawned and curled up in her bus seat to get comfy before falling asleep. She was woken about three hours later as they arrived at their first destination and they entered the Garden emporium...


	2. Chapter 2

Amalthea: *cackles evilly* Ok I finally watched the two Percy Jackson movies and read my Harry potter books right after which inspired this story! So please enjoy this Crossover! KON HIT IT!

KON: Amalthea does not own The Harry Potter series, Percy Jackson Series or any songs that appear in this fanfic. All she owns is the idea, Pairing, Family ties and her version of Fem-harry. Please vote in her poll plus Read and review her stories! Now On to SPARTA...I mean...ON TO THE STORY! Enjoy this little plot bunny!

Ch.2

Marina was surprised by all the statues in the place as her and the others had split up to look around, she then heard the hissing of Snakes and smiled as she hissed "_**Hello? Where are you**_?"

Medusa was surprised to hear Parsltongue being spoken and quickly lowered her glasses as she said back "_**Come child, I mean you no harm Speaker**_..."

Marina grinned and stepped out only to look confused at the woman when she knew she heard a bunch of snakes, Medusa chuckled then said as she revealed her "hair" "Hello"

Marina blinked then said "Cool! Are you Medusa?"

Medusa was surprised and said "Do you not fear me Speaker now that you know who I am?"

"Why should I? You're technically a person with Creature inheritance that's a little different than other people..."

Medusa laughed softly and invited Marina to sit next to her; Marina sat down as Medusa asked her what was going on the human world since she couldn't really leave the Emporium. Marina was happy to do so and Medusa listened in amusement when she caught a familiar scent from the child, Medusa then asked "Child, are you a child of Poseidon?"

Marina grinned sadly and told Medusa her story and that her father was possibly not aware she even existed, Medusa gave the child a hug and then Marina noticed the pearl on Medusa's wrist bracelet. Medusa noticed and said "Are you here for this pearl?"

Marina nodded and told her how Percy was being accused unfairly of stealing the lightning bolt when he hadn't and now His mom was being held hostage by Hades until the bolt was brought to him, Medusa smiled and then removed the pearl before handing it to Marina who looked at her in surprise. Medusa then said "You are an interesting child and I wish to see more of you if your camp will allow it in the future. Now go collect your brother and friends and go rescue your brother's mother."

Percy and Grover then charged into the clearing as Marina gave Medusa a hug and said "Thank you so much! Hopefully I will see you again!"

Percy was shocked as Medusa told them that Marina had granted them their freedom and she had the Pearl they were looking for, Marina giggled and said goodbye to Medusa as her brother followed with Grover and Annabeth. Medusa waved good bye then disappeared into the surrounding shrubbery, the teens then found a truck that still worked and hopped in as Percy asked "How did you manage to get the Pearl?"

Marina then said "She was just lonely and because I treated her with common curtsy, she treated me the same way."

Grover looked at Marina in surprise and then shook his head as he said "You are quite the kid, Marina...Medusa is feared for a good reason but I didn't think of doing that."

"Just because something seems monstrous, it doesn't mean it actually it is."

Percy laughed and said "She's got a point...I mean everyone considers Satyrs to be monsters in some cultures."

Grover then said "Very funny..."

Marina smiled as she then yawned and curled into her brother's side to go back to sleep, Percy smiled and wrapped an arm around her as Annabeth asked softly "So how long have you exactly known about each other?"

Percy quickly did the math and said "In total...17 days. Knowing she's my sister, one day."

Annabeth was surprised by that and said "You two are so close though!"

Percy laughed softly and said "We just automatically clicked when we first met and started talking about books and other stuff we like."

Annabeth smiled and said "I'm kinda glad she came with us...She's really sweet and it feels like kicking a Puppy if you hurt or offend her."

Four hours later...

After a near accident, Grover pulled into a local Motel and they got a room where Percy gently carried Marina who was still sleeping somehow, Percy put her on the bed nearest to the door and that designated it as the girls' bed while Percy would take the couch and Grover took the bed. They soon got some sleep after watching the news and Marina woke in the middle of the night, she sighed and eased out of the bed before going outside on the balcony. She then headed down to the pool and dangled her legs in the water as she let out a series of whistles, the tune was a soothing one and Marina looked up at the Night sky at all the stars she could see. She then began to softly sing a soft wordless tune that seemed to carry on the wind; she never noticed the creature watching her with its many heads from out in the dark field before it turned and went to go get in position to guard the second Pearl.

Two days later...

They arrived at their second destination in Nashville, Tennessee where Marina was looking around in wonder at the recreation of the Greek Pantheon. Marina smiled as she spotted the pearl at the same time as her brother, Marina then heard what her brother's plan for getting the pearl and chuckled as they went to hide. They waited what seemed like forever then slipped out of the bathroom where they saw some janitors cleaning the place, Annabeth was going to sedate them when Marina stopped her and said "Something doesn't seem right about them...let me try something."

Annabeth nodded and watched as Marina then told them to hide and watch the master, Marina then ran out of the bathroom as she began to cry for her Aunt and Uncle with large crocodile tears streaming down her face. The janitors all turned as one in surprise as Marina latched on to one of them and sobbed "My Aunt and Uncle abandoned me...They always threatened to do it and now they have! I have no way to go home to England..."

Percy was struggling not to laugh along with Grover and Annabeth when the Janitors then stood all next to each other suddenly and Marina stopped her tears as she suddenly hissed at them and the Janitors all went wide eyed, Annabeth looked confused along with the two males when the group of Janitors suddenly started merging into a very Rare fire Hydra. Annabeth made to move to rescue Marina when Percy stopped her and said "Wait, I think...she's talking to it..."

Marina stared the Hydra in the eyes and said in Parsltongue "_**Speak, for the last true heir of Slytherin has appeared before you...**_"

The hydra started at that then hissed "_**You're the child who was singing two nights ago...we heard you on our way here.**_"

Marina blushed and then asked "_**Why are you guarding the pearl?**_"

The heads of the Hydra all looked at each other then said "_**We have nowhere else to go where we won't be found...**_"

Marina blinked in shock then smiled as she asked "_**Do you have a smaller then a human form you can take on?**_"

The hydra nodded its heads and Marina then said "_**Why not come with us? I'm sure the camp could provide you with a home as long as you mean no harm to the camp inhabitants and help protect it...**_"

The hydra blinked then it started to shrink into the form of a wicked looking Doberman as he jumped and placed his paws on her shoulders to lick her face, Annabeth was shocked as Percy stepped out and the Doberman noticed but did nothing as Marina scratched his ears. Percy laughed as He offered the disguised Hydra a hand to sniff and got a small sniff before the animal returned its attention to Marina with a wagging tail stub, Annabeth then stepped out and said "I don't believe it...you completely tamed him somehow..."

Marina just laughed and said "Animals are easy to understand especially when you have the ability to speak to Dragons and other reptiles."

Grover eyed the hydra and said "he won't attack?"

Marina shook her head as she said "He's going to come with us...I'm sure the camp would like the extra security with him around..."

Grover's eyes nearly popped out of his head at that and said "How are we going to feed him though?"

The hydra gave Grover a rather dry look and Marina laughed as she said "He'll hunt for himself. Hydras love deer and if we are allowed, just give him a cow once in a while. Hydras actually only eat twice every four months and usually just survive off their elemental magic until they eat."

Grover and Annabeth looked shocked at that as the hydra then noticed Percy taking the pearl down with the pair of winged shoes Luke gave them, it just barked then Marina and Annabeth opened the door as they head for the truck. The disguised hydra hopped into the back of the pickup while Marina made sure he was comfy then she climbed into the cab with the others, they then headed to their next destination which was the Lotus in Las Vegas...

Marina had to smile at the beauty of Las Vegas at night when they spotted the Lotus and parked the Truck, Marina held on to the leash that was attached to the collar around their new Companion's neck as they walked into the Hotel/Casino. Marina sighed as all the staff tried getting her to eat a Lotus flower cookie but Marina refused because her disguised companion kept growling at the staff to leave her alone, she then started looking for her brother but grew worried when she couldn't find him at all. She had no idea the staff was keeping her away from her brother by making sure Percy and the other two didn't see her...

Five days later...

Percy finally came around and found his sister being harassed by a waitress to have a Lotus Cookie while the Hydra kept growling at the young woman, Percy then told the Waitress to leave Marina alone and grabbed Marina to take her to the others. Marina hugged her brother in relief as she began to sob gently and said "I thought you guys had left without me!"

Percy then asked "How long has it been?"

Marina told him "I don't know...they don't have any calendars or Clocks here!"

Percy then said "We need the others...come on!"

Percy and Marina raced towards the others as the hydra snapped at all the staff trying to stop them, Marina was quick to find and get Grover awake while Percy found Annabeth as the five raced towards the car at the front and climbed in. They quickly took off and began down the highway to find out it was only two days until the summer solstice, Percy and the others were shocked as Annabeth said "But it felt like only hours in there!"

Marina then asked "Where to next?"

They looked at the map and it said "Hollywood, California."

Grover then smirked and said "I can get us there in three-four hours. Hang on!"

Three hours later...

They had pulled up to the Hollywood Sign and were heading to the entrance when the hydra refused to go any further, Marina asked what was wrong and the Hydra told her that it could go no further but that he would meet her outside the camp once she was done the quest with her brother and friends. Marina smiled and hugged the disguised hydra around the neck as she whispered "Thank you so much for in Las Vegas..."

The hydra licked her cheek as she removed the leash and made to remove the collar when he told her not to and that it would split into a collar for each head due to its magic, Marina smiled as the hydra then said "_**Until we meet again Mistress...**_"

With that, the disguised hydra took off running the opposite direction towards the camp. Marina stood and smiled as she turned and they head towards the passage to the underworld...


End file.
